The present invention relates to acetal intermediates used in processes for producing 2-alkylidene-3-alkynals and 2-alkylidene-3-alkenals. Such aldehydes produced using the acetal intermediates of our invention are useful for augmenting or enhancing the organoleptic properties (aroma or taste) of consumable materials such as foodstuffs, tobacco products, and perfumes by adding to such articles quantities of one or more 2-alkylidene-cis-3-alkenals and/or 2-alkylidene-trans-3-alkenals as more particularly described in U.S. Pat. No. 3,988,487 issued on Oct. 26, 1976, which is a continuation-in-part of U.S. Application for Letters Patent Ser. No. 383,658 filed on July 30, 1973, now abandoned.
Pasternak et al. Bull.Soc.Chim., France (1966) at pages 356-361 discloses certain alkyl diacetals of cross-conjugated aldehydes but fails to set forth the utility of such acetals insofar as the organoleptic uses of the resulting hydrolysis products are concerned. Thus the Pasternak compounds have the structures: ##STR1## The only similarity between the Pasternak compounds and the compounds of our invention is that they are alkyl acetals of "tri-cross-conjugated" alkadienals. On the other hand, (i) the Pasternak reference does not disclose a utility of these acetals as intermediates for forming aldehydes having novel and unobvious organoleptic properites; and (ii) the compounds of Pasternak are acetals of methylene aldehydes rather than ethylidene aldehydes; and the compounds of Pasternak, rather than being straight chain hexenal acetals with an ethylidene substituent at the "2" position, are 2-methylene-3-methyl substituted butenal acetals or pentenal acetals.
British Pat. No. 1,025,046 published on Apr. 6, 1966, discloses certain unsaturated acetals and indicates that such acetals have a use in perfumery compositions, but these acetals have the formula: ##STR2## wherein the symbol R.sup.1 represents a hydrocarbon group or an oxygen-containing hydrocarbon group; the symbol R.sup.2 represents a C.sub.1 -C.sub.3 alkyl group or the symbols R.sup.1 and R.sup.2 together with the carbon atom to which they are attached represent a divalent carbocyclic group; the symbol R.sup.3 represents a hydrogen atom or a C.sub.1 -C.sub.3 alkyl group; the symbol R.sup.4 represents a hydrogen atom or a C.sub.1 -C.sub.3 hydrocarbon group; and the symbols R.sup.5 each represent an alkyl or alkenyl group or together represent an alkylene group, which formula is different in kind (rather than merely in degree) from the formulae of the compounds of the instant invention.
U.S. Pat. No. 3,463,818 shows unsaturated aldehydes having various floral odors and processes for preparing such compounds. Japanese published application 72/43526 shows the synthesis of terpene derivatives having orange-like odors, and hexadienal derivatives are shown. Wiemann et al, Memoires Presentes Soc. Chem., 1966, 1760, describe nuclear magnetic resonance studies of some conjugated dienals, and a number of these compounds, including 2-ethylidene-3-pentenal are shown. 2-Propenyl-2-pentenal is mentioned in Chem. Abstracts 35, 6238.
West German published application 1,951,883 is said in Chem. Abstracts 75, 5246 to show preparation of dienals useful as perfumes. Tiffeneau et al, Comptes Rend. 204, 590 show the preparation of 2-alkylidene-3-alkenals.
U.S. Pat. Nos. 3,272,873; 3,453,317; and 3,493,619 show processes for preparing unsaturated aldehydes or for treating such aldehydes. U.S. Pat. No. 3,520,936 shows production of an unsaturated aldehyde, and U.S. Pat. No. 3,542,878 shows an aldol condensation using a tin catalyst.
Odiger et al Annalen 682, 58 (1955); Corey et al, J.Am.Chem.Soc. 90, 6816; and Wittig et al, Chem Ber. 94, 676 show "alkylidenation" reactions utilizing phosphorous compounds.